Previous research has demonstrated that flow disturbances distal to subtotal vascular stenoses in the descending thoracic canine aorta and in laboratory models may offer an indication of the presence of localized atherosclerotic arterial disease at a relatively mild stage of development. In addition, recent progress has yield improvements in Doppler ultrasound blood velocity measurement which will allow noninvasive measurement of flow disturbances. The present research is designed to utilize these previous findings as a basis for study of the carotid arterial complex in human subjects, after first gaining additional experience in canine measurements. The objectives are to provide fundamental studies of the flow patterns in the region of carotid bifurcation for normal and diseased subjects, utilizing previously developed mathematical methods of characterizing flow disorder, and to evaluate the results to decide whether the techniques offer an improvement over currently available methods for the noninvasive diagnosis of carotid vascular disease.